1. Field of Invention
My invention relates generally to electrically powered heating mats, and more particularly to a selectively positional array of thin modular mats powered by low voltage electrical current.
2. Background and Description of Prior Art
Electrically powered mat-like devices have long been known and used for generating heat for various purposes and through the course of their development such devices have become quite sophisticated and specialized for particular purposes. The instant invention provides a new member of this class of device that is particularly adapted for use on generally horizontal surfaces to melt environmental ice or snow that might otherwise accumulate thereon.
The accumulation of ice and snow on outdoor structural surfaces traversed by people is an ever present problem in the Northern climes during winter weather. The problem in general is resolved by physical removal of the ice and snow, and this presents a reasonably satisfactory solution that is practically obtainable for open horizontal surfaces of some areal extent where normal mechanical removal methods may be readily applied. The problem becomes more acute, however, in smaller adjacent but discontinuous areas, and especially such areas that have substantial or concentrated foot traffic, like door steps and entryways to structures which present a perennial problem for snow removal.
One approach to the debris removal from such areas has been the use of heating, sometimes by heating the structure involved or at least its surface by internal means or commonly by application of some heat generating device to the surface such as a heated mat or pad. Various, such heated mats have heretofore become known and in the course of their development they become quite sophisticated, though none seem to have satisfactorily resolved all problems associated with their use and purpose. The instant invention provides a new and novel member of this class of device that addresses unsolved problems.
The configurational embodiment of heated mats is critical to their practical utility and has not been well addressed by prior devices. Such a mat must be relatively thin to allow use on surfaces over which other objects must pass, such as a door mat over which a door may move. Additionally, a mat of any substantial thickness may disrupt the normal and habitual use of an area being traversed by an individual to cause slipping or falling, especially if used on part but not all of that area or on a flight of stairs or similar platforms. The mat also must be quite rigid to maintain configurational integrity during use, reduce potential slipping or failing during use, prevent slipping or falling, and allow objects to be moved thereover when in contact therewith.
The areal size and configuration of a mat for reasonable utility must be such as to fit on a substantial number of surfaces on which it is to be used. If a mat extends beyond the periphery of a supporting surface, it will provide problems in use and those problems will tend to substantially reduce its reliability and useful life. I resolve these problems by providing a rectilinear mat having an areal size and peripheral configuration not larger than the same parameters of ordinary steps and one with a rigid back formed of fiberglass fibers embedded in a polymeric matrix for strength, as opposed to the relatively flexible prior structures of greater thickness and often substantially greater areal extent.
Such a mat with a rigid back generally requires some means for positional maintenance to avoid motion between it and a rigid supporting surface during use. This requirement for positional maintenance has often been ignored or alleviated in the prior art by providing a flexible mat, but this solution is not effective. In contradistinction I provide alternative fastening by adhesive patches or mechanical fasteners extending through the mat and into fastening engagement with an underlying supporting surface. This type of fastening in the harsh environments in which heating pads are commonly used provides substantially greater potentiality of positional maintenance of my mat that varies almost directly with its safety of use.
Functionally prior mats have experienced difficulties in providing uniform heat over the entire mat surface and in providing sufficient heat to melt ice and snow without expending excessive energy. The prior art has either tended to ignore this problem, solved it by providing excessive amounts of heat to provide a sufficient heat level, or have attempted to use some type of thermostatic control. The provision of excessive energy to provide minimal required heat in non-uniformly heated areas is not economically feasible and thermostats have not been particularly effective because they generally do not measure heat at points where it is required nor do they measure the amount of that heat necessary to accomplish proper functioning. Thermostats generally measure the temperature of a mat in a limited area which is not necessarily related to heat work or its areal uniformity.
I solve this problem by providing a heating element that is formed of a continuous strip of electrically resistive metallic foil that is uniformly arrayed over the entire mat area and covers a substantial portion of the mat to provide substantially uniform heat over the entire mat surface. This type of heating element provides secondary benefits. The foil allows electrical powering of the heating mat with low voltages of either direct or alternating current and has a high efficiency ratio to use a minimal amount of electrical energy during periods of continuous operation. The structure of my pad will provide tertiary benefits in that its lower portion is somewhat thermally resistive and tends to direct substantially more of the heat produced by the heating element upwardly than downwardly, so that the heat produced is effectively used in melting functions rather than in heating an underlying supporting structure.
Areas from which ice and snow are desired to be removed often are non-contiguous and of varying configuration and positional array. Most prior heating mats have serviced only a single contiguous area and those that have become known to service multiple spacedly related areas have been adapted to service only such areas as are of predetermined configuration and areal relationship. My invention in contradistinction provides a plurality of modular heating mats that may be spacedly arrayed as desired in relationship to a linear conductor furnishing power to the plural mats. This function is allowed by the particular construction of the electrical powering system and the interconnection of individual mat modules thereto.
Each modular unit is interconnected in electrical parallel with a two-wire conductor by a so-called "vampire" connector which allows releasably adjustable positioning anywhere along the conductor. Such vampire connectors provide two pointed contact elements that pierce the insulation on a conductor to contact the conducting wires carried therein to power the individual module, but yet allow removal and replacement of the connector as desired with subsequent reformation of the resilient insulating element about the conducting wires. This type of interconnection is allowed especially by reason of the low voltage power supply of my system which provides substantial safety from injury caused by shorts or improper or incomplete resealing of the insulation about the electrical wires. The modular nature of the several heating pads allows use of my system on surfaces of varying configurations by use of varying numbers and arrays of modules to make system use almost universal in nature.
Most heated mats heretofore known that have been electrically powered have used ordinary household type electric current providing electrical power of a single phase alternating nature at one hundred twenty volts. My invention is distinguished from these devices by providing resistive heating elements that are powered by current preferably of not more than fifty volts and of either alternating or direct nature. This type of current not only avoids wastage as aforesaid but also is universally safe for use with humans or animals, even in the severe environments in which heating mats are commonly used. Even if an electrical short circuit should accidentally occur or if current should pass through a user to some ground source, the voltage is low enough so as to cause no physical injury or harm to either human or lower animal. The lower voltage also limits the amount of power that is distributed to the several mat units and provides a maximum potential power to provide an absolute limit of power usage for automatic non-thermostatic control. The powering system may provide a transformer so that ordinary commonly available household current may be used to power the system and includes traditional switching means to maintain the system in either condition for a predetermined time interval.
A heated mat system is particularly adapted for use on or about entry portals where foot traffic is concentrated and configurational parameters commonly quite limited, such as about doorways and on stairs leading thereto or therefrom in both structures and vehicles. With use of my mat structure in vehicles, it should be particularly noted that many commercial vehicles provide a low voltage powering system that is available for powering the system and if not, powering systems provided may be easily transformed to a low voltage current. If desired, my invention may be operated at either higher or lower voltages with appropriate modification of the electrical components.
My invention resides not in any one of these features per se, but rather in the synergistic combination of all of the structures of my system that combine synergistically to provide the functions necessarily flowing therefrom, as herein specified and claimed.